The present invention relates to a novel material for useful as an oxygen permeable soft contact lens, and more particularly to a soft contact lens material having a surface excellent in a hydrophilic property and moreover having a high oxygen permeability prepared by copolymerizing as main components, a polyorganosiloxane having a polymerizable group and a hydrophilic group in the molecular side chain and a hydroxyl group-containing hydrophilic monomer in which hydroxyl group is silylated prior to polymerization, and conducting the desilylation to produce hydroxyl group.
An excellent oxygen permeability is one of the most important conditions required for contact lens materials.
The following three methods hitherto have been proposed to improve the oxygen permeability.
(1) A process for improving an oxygen permeability wherein a behavior of water impregnated in a lens material is utilized by increasing the water content. PA0 (2) A process for applying materials hitherto known as materials excellent in an oxygen permeability, for instance, a silicone rubber material, and the like, to contact lens materials. PA0 (3) A process for using a silicone-containing monomer known as an oxygen permeable monomer, for instance, siloxanylalkyl (meth)acrylate monomers, and the like. PA0 (a) a polyorganosiloxane (A) having polymerizable groups and hydrophilic groups in the molecular side chains, each of which has a polymerizable group and a hydrophilic group, and PA0 (b) a monomer having silylated hydroxyl groups as main components, and subjecting the resulting copolymer to desilylation.
According to the above process (1), the oxygen permeability is improved by increasing the water content. On the contrary, the material has some problems such as a remarkable deterioration of mechanical strength when it is impregnated with water and an easiness to be contaminated when it is used as a contact lens.
A silicone rubber material which is most often used in the above process (2) has a water repellency unique to the material. When it is used as a contact lens which is contacted with a cornea, the lens surface shows no good affinity for the lacrimal fluid on the surface of cornea. Therefore, the lens surface is generally modified to have hydrophilic property by corona discharge treatment. However, the thus treated lens surface has some problems such as in the durability, and consequently, it causes trouble in the cornea when it is used for a long period of time.
Most of the materials used in the process (3) are hard materials, and they are useful to obtain so-called an oxygen permeable hard contact lens. However, the contact lens has some problems such as an uncomfortable feeling upon wearing caused by hard materials, characteristic of the hard contact lens made of polymethyl methacrylate which hitherto has been used.
It has been attempted to impart the hydrophilic property which is stable for a long period of time onto the surface of the contact lens by not modifying only the surface layer by means of physical surface treatment to decrease the surface repellency, but modifying the material itself in order to modify the silicone rubber material having excellent oxygen permeability and softness into a suitable contact lens material.
For instance, Japanese Unexamined Patent Publication No. 108881/1980 discloses that a hydrophilic siloxane having a side chain containing a polymerizable group and a side chain containing a hydroxyl group (a hydrophilic group) in a polyorganosiloxane chain is synthesized and then the hydrophilic siloxane is copolymerized with the hydrophilic siloxane independently or with other hydrophilic monomers to improve the hydrophilic property, and Japanese Unexamined Patent Publication No. 94323/1981 and No. 94324/1981 disclose that a polyorganosiloxane having a polymerizable group in the end of the molecular and a side chain having a hydrophilic group such as hydroxyl group is synthesized and then a contact lens made of polyorganosiloxane having an improved hydrophilic property is obtained by preparing a polymerization product containing the polyorganosiloxane as a main component. Also, Japanese Unexamined Patent Publication No. 102914/1984 discloses that a polyorganosiloxane having a polymerizable group in the chain of the polyorganosiloxane is synthesized through urethane, thiourethane, urea or an amide bond, and then a polymerization product having an improved hydrophilic property is synthesized by copolymerization of the polyorganosiloxane and various monomers.
In all prior arts mentioned above, a hydrophilic group is induced into a polyorganosiloxane which is used for a contact lens material, and the hydrophilic group is chemically bonded in the molecule, and therefore, the improvement of the hydrophilic property is recognized. However, in order to modify the water-repellency (hydrophobicity) that a polyorganosiloxane useful for a contact lens material used in contact with a cornea inherently possesses into the hydrophilic property, it is preferable to copolymerize with other hydrophilic monomers furthermore.
As disclosed in the above publications, it is difficult for a hydrophilic monomer to be uniformly admixed with a polyorganosiloxane by merely mixing them without any treatment. Also, when such a system is subjected to polymerization, the hydrophilic property is improved. However, when it is used for a contact lens, there is a defect such as an extreme lowering of the optical transparency, particularly in water (at wetting). The reason why the transparency is lowered has been considered to be as follows. Since generally the compatibility of the polyorganosiloxane having a high hydrophobic property and a hydrophilic monomer is not good and they are not copolymerized uniformly, a hydrophilic portion and a hydrophobic portion are formed in phase separation structure in a polymer molecular, and the refractive index of each separated phase is different from each other, and therefore the transparency is lowered.
The present invention is accomplished in order to obtain a polymer having a surface excellent in a hydrophilic property (wetting property) while maintaining a high oxygen permeability and a softness of a polyorganosiloxane useful as a contact lens material, and in order to solve such problems as the polyorganosiloxane having a polymerizable group and a hydrophilic monomer not being copolymerized uniformly, and therefore the obtained copolymer becomes non-uniform, or the optical transparency of the copolymer is lowered, particularly in water (at wetting).
A further object of the present invention is to provide a material having a suitable dynamic property (strength) and substantially a water-non-absorptive property or a lower water-absorptive property.
These and other objects of the present invention will become apparent from the description hereinafter.